1. Field of the Invention
The present invention relates to a barometric altimeter, and more particularly to a barometric altimeter employing a solid state pressure transducer, located in physical proximity to a pitostatic tube, with means for developing an accurate digital representation of the altitude as the function of a signal derived from the pressure transducer.
2. The Prior Art
Present day aircraft typically use aneroid barometers, which employ pressure responsive devices such as a Bourdon tube or the like, to transduce pressure into mechanical movement so that the altitude is indicated, as a function of pressure, by movement of a needle or the like on a panel meter. The pressure transducer is located at the site of the meter, and relatively long lengths of tubing extend from a pitostatic tube to the site of the instrument, in order supply the pressure to the transducer.
Such barometers lack accuracy, and involve a considerable amount of tubing, especially in the case of large airplanes having multiple pitostatic tubes. An airplane such as the Boeing 747 employs a considerable number of pitostatic tubes or ports, and at the present time long lengths of tubing are required to extend from each of the pitostatic ports to a pressure transducer located remotely therefrom.
In addition to the expense involved in the construction of present day systems, there is also considerable effort required to insure that the tubing does not leak when it passes through an area (such as the interior of the aircraft) having a pressure which differs from the pressure within the tube. Leakage in such an area of course would lead to an inaccurate result. Other maintenance is also necessary, which increases the cost of maintaining the system.
In addition, the accuracy of such systems is limited, and therefore must be supplemented by more accurate altitude measuring apparatus when precision in altitude measurement is critical.
Several attempts have been made to design altimeters employing solid state transducers, in place of the pressure-mechanical transducers, but since the electrical transducers are located remotely from the pitostatic port, they still require a length of conduit interconnecting the transducer with the port. Thus the problem involving the tubing or conduit has not been overcome.
In addition, attempts to use digital techniques for altimeters have not met with success because a relatively high storage capacity is required for a processor to develop an accurate digital representation of altitude from a pressure responsive signal. This has tended to make such apparatus complicated and expensive, so that they have not been able to displace the traditional aneroid barometers incorporating large quantities of tubing and pressure-mechanical transducers.